The present invention relates to fluid flow control apparatus.
The control of the extraction or ingestion of fluid from or to a well in a fluid (e.g. oil or gas) extraction system is effected by chokes which have variable orifices in the production tube wall, typically operated by hydraulic or electric actuators. FIG. 1 shows a sectional view of a well with a choke fitted within a casing 1 of a borehole 2 and sealed with a packer 3. The choke body 4 of the choke is larger in diameter than production tubing 5 in order to accommodate a mechanical drive for controlling variable orifices 6 of the choke and its control and monitoring electronics around the circumference of the tubing 5. Thus, the standard sizes of the casings used in the fluid extraction industry determine the maximum diameters of choke bodies. In order to maximise the output extraction rate of the well, the maximum diameter of production tubing 5 is utilised. FIG. 1 also illustrates an extraction area 7 with a sand screen 8 fitted, as is typical. Invariably, the external diameter of the sand screen 8 is also limited by the bore of the casing 1, in order that it can be passed down it during installation.
Thus, as shown in FIG. 2, in the situation where there are two extraction zones 9 and 10, each with a respective one of sand screens 11 and 12, typically two chokes are fitted. Since the outer diameter of each of the choke bodies 13 and 14 does not allow it to pass through a sand screen, and/of the choke assembly is often too long to be accommodated by a sand screen, the two chokes are arranged in series as shown in FIG. 2, which shows the extracted fluid from zone 9 passing through the sand screen 11 to the variable orifices 15 of the lower choke having choke body 13 in a conventional manner, as shown by the arrows on the Figure. However, the extracted fluid from zone 10, through the sand screen 12, has to pass through the space between the choke body 13 of the lower choke and the well casing 1, in order to pass through variable orifices 16 of the upper choke having choke body 14. An alternative arrangement is to fit a choke of smaller diameter, and thus smaller production tubing bore, in the position of the upper choke. However, these typical arrangements create a number of problems:
1/ The flow of fluid between the choke body 14 and the casing 1 is seriously restricted by the relatively small gap between them.
2/ If the upper choke having choke body 14, is replaced with a choke of smaller dimensions, then a major redesign of the choke is required and the production flow tubing for the extraction from zone 10 is reduced.
It should be noted that when ingestion of fluid, typically water, into the well is required typically for maintenance, the same problems occur.
According to the present invention, there is provided apparatus for use in controlling the flow of fluid between first and second zones and a common region, comprising:
a first passageway, for providing a first fluid flow path, between the first zone and the common region, in use of the apparatus; and
a second passageway, outside the first passageway, for providing a second fluid flow path, between the second zone and the common region, in use of the apparatus, the first passageway being provided with first flow control means, for controlling the flow of fluid between the first zone and the common region and the second passageway being provided with second flow control means, for controlling the flow of fluid between the second zone and the common region.
The first and second passageways are preferably substantially concentric with each other.
The first and second control means may each comprise at least one orifice between the respective passageway and the common region.
The first and second passageways may be provided by first and second tubular members.
There may be sealing means between the first and second passageways for isolating the first and second flow paths from each other.
The apparatus may include a third passageway (for example provided by a tubular member) in fluid communications with the common region, which third passageway is preferably substantially co-axial with the first and second passageways.
There may be sealing means between the third passageway and the first and second passageways.
The third passageway may be in communication with the common region via at least one (preferably non-variable) orifice and in this case the or each such orifice may be in a wall of such tubular member providing the third passageway.
Each of the first and second passageways may be provided with means for varying the rate of fluid flow through the respective flow control means.
Apparatus according to the invention may be in the form of a choke assembly for use in controlling the flow of fluid between first and second zones and production tubing in a production well.